Vulcanization of polyurethane elastomers with diisocyanates



United States Patent O VULCANIZATION OF POLYURETHANE ELASTO- MERS WITH DIISOCYANATES Frederic B. Stilmar, Wilmington, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, DeL, a corporation of Delaware No Drawing. Application February 17, 1955 Serial No. 489,000

15 Claims. (Cl. 260-75) 'This invention relates to the preparation of polyurethane elastomers, and more particularly to a method of curing or vulcanizing such: products.

Curable elastomers having valuable properties may be prepared by reacting a long-chain polyalkylene ether glycol with a molar excess of an organic diisocyanate to form a linear polymer containing urethane linkages, and then reacting this polymer with a chain-extending agent containing a plurality of active hydrogen atoms, such as water, a diamine, a hydroxyamine, and the like, as dis closed and claimed in copending application Serial No. 365,270 of Hill, filed June 30, 1953. Similar products are obtained by reacting together a high molecular weight organic bischloroformate, an organic diamine and phos' gene, as described in copending application Serial No. 461,657 of Carter and Ernsberger, filed October 11, 1954. Other useful polyurethane elastomers may be prepared by reacting a high molecular weight polyester with a molar excess of an organic diisocyanate and a chain-extending agent, as described for example by Bayer et al.

,in Angewandte Chemie, 62, 57-66 (1950).

Products of this type may be cured by heating, ordiinarily under pressure, if the reaction .product contains :freeisocyanate groups. Under these conditions, the free isocyanate groups are believed to react with active hydrogen atoms in the polymer to produce cross linking of the polymer chains. If the proportion of reactants has been such that few free isocyanate groups are present, or if the uncured reaction product has been stabilized against premature curing by the addition of some material such as a primary or secondary amine which reacts with and ties up the free isocyanate groups, it is necessary to add a curing agent prior to heating to effect vulcanization. The curing agents ordinarily employed arediisocyanates. When the conventional diisocyanates such as the tolylene diisocyanates are used as curing agents, difiiculty is often encountered because of the great reactivity of these compounds which results in premature curing or scorching" of the elastomer before the curing agent can be thoroughlyincorporated. This results in a non-uniform cure and interferes with the production of molded articles, since it may not be possible to force the partially cured product to fill the mold completely. The problem of scorching is partly overcome by the use of diisocyanates in which each isocyanate group is ortho to a substituent on the aromatic ring to which the isocyanate group is attached. Substituents on the aromatic ring in the ortho position exert an inhibiting effect .on the reactivity of the isocyanate group, and compounds of this type consequently permit better control of the vulcanization reaction. Examples of this type of compound are the 1,3-bis(3-isocyanato-4-alkylphenyl)ureas and the corresponding compounds in which an alkoxy or a chlorine atom take the place of the alkyl substituent. Even with these compounds, however, scorching may occur on the rubber mill before the agent is completely ,rnixed in.

his an object of this invention to provide a method for phenylene curing polyurethane elastomers of the types hereinafter described which reduces the tendency toward scorching and which makes possible careful control of the de-' sired degree of vulcanization.

It has now been found that, according to the present invention, a stable uncured polyurethane reaction prodnot which is curable by heating with a polyisocyanate and which contains substantially no free isocyanate groups may be cured with reduced danger of scorching by first incorporating therewith from 0.5 to 2% by weight of an arylene diisocyanate in which one only of the isocyanate groups is ortho to a substituent on the aromatic ring, thereafter incorporating from 1 to 20% of an arylene diisocyanate in which each of the isocyanate groups is ortho to a substituent on the aromatic ring to which the isocyanate group is attached, and heating the mixture until a cured elastomer is formed.

In a preferred embodiment of this invention, the reaction product of a polytetramethylene ether glycol having a molecular weight between 750 and 3500, a molar excess of a to lylene diisocyanate, and water, said reaction product containing substantially no free isocyanate.

compound 2,4-tolylene diisocyanate, it is entirely unexpected that a still further improvement in resistance to scorching is obtained by treating the uncured reaction product first with a small amount of this latter unsymmetrical type of diisocyanate and then with the former symmetrical type. The mechanism of this effect is not fully understood, but it is supposed that the more.

reactive isocyanate group in the unsymmetrical compounds is able to tie up the more reactive groups present in the polymer, possibly amino groups, and thus to prevent their reacting with the subsequently added curing agent.

The arylene diisocyanates in which one isocyanate is more reactive than the other include compounds having the formula R-NC 0 in which R represents a lower alkyl, lower alkoxy, or phenoxy radical or a halogen atom. Typical members of this class useful in the process of this invention are 2,4-tolylene diisocyanate, 4-tertiary-butyl-m-phenylene diisocyanate, 4-methoXy-mphenylene diisocyanate, 4- propyloxy in phenylene diisocyanate, 4 chloro-mdiisocyanate, 4-bromo-m-phenylene diisocyanate and 4-phenoxy-m-phenylene diisocyanate. Members of this class in which the substituent R contains no more than about 6 carbon atoms are preferred.

The diisocyanates having each isocyanate group shielded by an ortho substituent, which are useful as the second curing agent in the process of this invention, include 1,3- bis(isocyanatoaryl)ureas of the formula:

No 0 No 0 in which R is lower alkyl, lower alkoxy or chlorine, e. g,, 1,3-bis(3-isocyanato-4-methy1pheuyl)urea.

Patented Oct. 28, 1958 The preferred amount of each of the diisocyanate curing agents used will depend somewhat on the nature and previous history of the uncured elastomer which is to be treated. It is desirabie thatfrom 0.5 to 2% by weight of the arylene diisocyanate havin one unshielded isocy'ana't'e group be used. With less than 0.5%, no substantial improvement is secured, While at amounts greater than 2%, the product may begin to be more rather than less susceptible to scorching, due to the high reactivity of this diis'oc'yanate'. The amount of the second diisdcyanate is somewhat less" critical and may vary from 1 to 220%, although from 1 to 8% is ordinarily suflicient'. 111' general the rate of cure increases with higher amounts of the diisoeyanate cn'ri'ngage'nt. v I

In carryin out the process of this invention, the un-' cured elastomer'ic reaction product is mechanically worked on a rubber mill or other mixing; equipment until it forms a smooth sheet. Compounding agents such as carbon black, plasticfzer, and the like are added as desired; The necessary amount of the di'iso'cyanate having one unshielded isocyanate group is added while milling is continued and, after thorough mixing, the proper amount o'f'the diisocya'nate having both isocyanate groups shielded by ortho substitute is milled in. The compounded mass is sheeted off the mill .and cured, ordinarily by" heating; Temperatures of 90 to 150 C. are normally used and only enough pressure is required to force the compounded elast'o'mer' into the mold. This may range from 30 to 40 pounds up to 3000 pounds per square inch. At the temperatures mentioned, 15 to 45 minutes are usually suificient to produce a cure. Curing may be effected without the application of pressure. The compounded elastomer' may be sheet'ed out and calendered either alone or onto a substrate such as a plastic or textile and may then be heated to produce the cure; It is also possible to cure the product Without using either pressure or'elevated temperature, but this ordinarily requires substantiallylonger times.

The polymeric reaction products which may be cured according to this invention include those which are prepared from polyalkyle'ne ether glycols, diisocyanates and chain-extending'agents', as disclosed and claimed in pending application Serial No. 365,270 of Hill, filed June 30, 1953. The term polyalkyle'ne ether glycol as used throughout the specification and claims refers to a polyalkylcne ether which contains terminal hydroxy groups. These compounds are derived from the polymerization ofcyclic e'thers such as alkylene' oxides or dioxolane or from the condensation of glycols. They are sometimes known as'polyalkylene' glycols or olyalkylene oxide glyc'ols'. Those useful in preparing the products of this invention may be represented by the formula HO(RO),,H, in which R stands for an alkylene radical and n is an integer sufficiently large that the molecular weight of the compound is at least 750, i.- e., large enough that the polyoxyalkylene group -(RO).,, has a formula weight of at least 732. Not all" of the alkylene radicals present nce'd'b'e' the" same. Glycols containing a-mixture of radicals', as in the compound HO('CH OC H O),,H can beused These glycols areeither viscous liquids or waxy solids. To be of value in preparing elastomers according to this invention, the molecular weight of the glycol should-be at least 750 and may be as high as 10,000. It preferably between'750 and 3500. Polytetramethylene ether glycol, also known as polybutylene ether glycol, is the preferred glycol. Polyethylene ether glycol, polypropylene'ether glycol and poly-l,Z-dimethylethylene ether glycol are representative of other operable compounds.

Any of a wide variety of diisocyanates may be used in the polymerization. Aromatic diisocyanates, such as 2,4-tolylene diisocyanate, 4,4-methylene-bis('phenyl isocyanate), 1,5-naphthylene diisocyanate and m-phenylene diisocyanate, are preferred. Aliphatic compounds such aslfexa'mctliylene diisoc'yanat'e and tetramethylene diisocy- 4 anate, and alicyclic compounds such as 1,4-cyclohexylene diisocyanate are also operable.

The chain-extending agent contains a plurality of active hydrogen atoms, no more than two atoms in the molecule having active hydrogen attached thereto. It is preferably water. By active hydrogen atoms is meant those hydrogen atoms which display activity according to the well-known Zerew'itinoff test as described by Kohler in J. Am. Cherrr. Soc., 49 31'81 (1927). When water is employed as the chainextender it is capable of reacting with two isocyanate groups with the evolution of carbon dioxide to form a urea group linking the polymer fragments to which the isocyanate groups were attached. Urea linkages are also formed if a diamine such as 2,4-tolylene-diamine of ethylene diamine is used as the chain-extending agent. Qther useful chain extenders include ethylene glycol, adipamide, p-aminobenzoic acid,

monoethanolamine, 1,4-cyclohexanedisulfonamide, succinicacid; and hydroxypr'opionic acid.

In the preparation or the'polym'er, an excess of the diisocyanate over the polyalltylene' ether glycol is used, whicla may be only a slight excess or may be up to a 12:1 molar ratio. The glycol and the diisocyanate are ordinarily reacted by heating with agitation at a temperature of betweenand 1 20 C. The chain-extending agent is then added and heating and mixing are continued at about to (3-. During this period the molec-' ular weight of the reaction product increases and the mass gradually forms rubbery chunks. It is then removed front the mixer and sh'eeted out on a rubber mill. If all of the" free isocyanate groups have not reacted with the glycol or the chain-extending agent, the elastomer will have a tendency to cure rather rapidly. Ifthe reaction product is to' be" stored prior to the final curing step, it is then necessary to stabilize" it by adding some material such as primary or' secondary nitrogen base in amount suflicient to react with the remaining free isocyanate groups, as disclosed and claimedin application Serial No. 379,291 of Nelson" e't-al, filed September 9, 1953';

Thisstabi'lized polymer and the self-stabilized polymer which results when enough glycol and chain-extending" agent have been used to tie up all the isocyanate groups may be stored for considerable periods without losing their ability to form a smooth band when milled on a rubber mill.

Instead of the hydrocarbonportion of the polyether glycols used in formingthese products being entirely alkylene, the compound can contain arylene or cycloalkylene radicals together with the alkylene radicals as,- for example, in-th'e condensation product of a polyalkyl-' cue ether glycol-with d',a'-dibromo-p-xylene in the pres ence of alkali. In such products, the cyclic groups inse'rted in thepolyether' chain are preferably phenylene naphthyle'r-ie or-"cyclohexylene radicals or these radicals containing alky' l or alkylene-subs'titu'ents, as in the tolyl ene, phenylethylene or xylylene radicals. Elastoiner's made using} p'clyalkylene-arylene or polyalkylene-cy'cloalkylene ether glycols have' improved freeze resistance as compared with the-corresponding elastomers containing nocyclic radicals.

Another class of glycols us'eful'in making polyurethanes curable according to this invention are the'poly'etherpolythio'et'he'r glycols. by the formula HO(QY),,H in which Q represents hydrocarbon radicals, at least some of which are alkylene, Y' represents chalco-gen atoms, some of which are sulfur and therest oxygen, and n is an integer large enough so that the glycol has ,a molecular weight of at least 75.0.

These products maybe made by condensing together having a molecular weight of at least 750 and havihglat Such glycols maybe represented Each end a functional group, said functional groups being connected by a hydrocarbon or a halogen-substituted hydrocarbon chain. The functional groups at the ends of the long chain compound are hydroxyl groups. The bydrocarbon chain connecting the functional groups is free of substituents other than halogen atoms and monovalent hydrocarbon radicals, such as methyl, phenyl, etc., preferably containing no more than 8 carbon atoms. Such long chain compounds are obtained, for example, by polymerizing ethylenically unsaturated monomers in the presence of free radical catalysts such as the aliphatic azo dinitriles or dicarboxylates. The most suitable ethylenically unsaturated monomers are conjugated dienes such as butadiene, isoprene, 2-chlorobutadiene and the like. Mixtures may be used. For example, styrene or isobutylene may be copolymerized with a diene to give the long chain skeleton. The carbon chain in the long chain compound may be saturated or unsaturated.

Also included in the products which may be cured according to this invention are those made from a high :molecular weight, substantially linear polyester, an or- .ganic diisocyanate, and a chain-extending agent of the type previously described. Products of this sort are described in the aforementioned Bayer article in Angewandte Chemie, and in U. S. Patents 2,621,166, 2,625,531 and 2,625,532. The polyesters must have molecular weights of at least 750 and are prepared by reacting together glycols such as ethylene glycol, 1,2-propylene glycol, 2,3-butylene glycol, and 1,6-hexylene glycol, and dicarboxylic acids such as adipic, pimelic, sebacic, oxalic and phthalic acids and decamethylene dicarboxylic acid. The polyesters may be represented by the formula in which R and R are hydrocarbon radicals derived from the glycol and dicarboxylic acid respectively and n is an integer large enough that the molecular weight of the compound as a whole is at least 750 and that the polyester group --[R.OOC.R.COO],,.RO-- has a formula weight of at least 732. The polyester resulting from reaction of adipic acid with a mixture of ethylene and propylene glycols is preferred. In the preparation of these polyesters, the glycol is used in at least slight excess so that the polyesters contain terminal hydroxyl groups which are available for reaction with the isocyanates. The same diisocyanates, chain-extending agents and reaction conditions useful in preparing elastomers from the polyalkylene ether glycols are also useful with the polyesters.

Elastomers which are similar to those formed from the reaction between long chain glycols of the types mentioned above, diisocyanates and water may be made from the reaction of a high molecular weight organic bis-chloroformate, an organic diamine and phosgene, as described and claimed in pending application Serial No. 461,657 of Carter et al., filed October 11, 1954. These products may be cured advantageously by the process of l this invention.

It is obvious from the above-described methods by which the uncured polyurethane reaction products may be prepared and the reactants used that these products will contain a plurality of intralinear radicals of the formula glycols and polyester glycols of the formula i i H0-ER-0O-RO0 wherein R and R are hydrocarbon radicals and n is an. integer.

The tendency of the compounded elastomers to cure prematurely or to scorch may be measured by the follow-- ing tests.

130 C. MILL SCORCH TEST In this test, 10 to 12 grams of the compounded elas-- tomer containing the diisocyanate curing agent are put on a 2" x 6" rubber mill at about 30 C. and milling is begun. The temperature of the mill roll is raised to -l00 C. with steam and held there for about 2 minutes. The mill roll temperature is then raised to 130 C. and held at that temperature. Milling is continued until the sample scorches or until a given time elapses without any scorching. Scorch is indicated by the appearance of holes in the band on the roll, the loss of tack and nerviness of the band and the formation of a dry crumbly bank at the nip of the rolls. Where scorching is severe, the polymer may crumble and fall oif the mill. Scorch-resistance according to this test is measured in terms of the number of minutes until scorch is apparent, beginning when the temperature of the roll reaches 130 C.

EXTRUDER SCORCH TEST compounded stock. The stock is then added and when it begins to emerge through the die, heating on the worm. and barrel is discontinued and cold water is passed through, but the head is held at 93 C. with steam. The extruded strip is fed back into the feed barrel. The

. amount of composition used is such that there is on the average a 4 minute residence time in the extruder and 1 minute time on the outside before being fed back in. As extrusion continues, the strip is at first slightly nonuniform because of incomplete mixing. As extrusion continues, the band becomes smooth and homogeneous until the point when scorching begins. At this time a gradual surface roughness develops which soon becomes pro nounced.

MOONEY SCORCH TEST This is a standard method of determining the curing characteristics of elastomers by use of a shearing discviscometer. It is ASTM Test D-Ol77-49 T as described. in ASTM Standards on Rubber Products, published by the American Society for Testing Materials. This test measures the change in viscosity of the curable mixture as a function of time, While the sample is held at a specific temperature. The compositions described in the examples which follow were tested at C. using a small rotor- The process of this invention is illustrated by the fol'- lowing examples, in which parts are by weight unless otherwise indicated.

Example 1 i There are mixed in a Werner-Pflciderer mixer 500 parts of polytetramethylene ether glycol having a molecular' weight of 2400 and containing 0.02% water and 44.5

parts of .2 ,4.-tolylene diisocyanate for 3.5 hours. while. maintaining a.temperature. of 130 C on-the jacketof; the mixer. 755 parts; of m-tolylene diamine are" added, andrnixing'is'"continued for thirty'minutesmore. The. product is then'a taffy-like mass which is removed from the mill after cooling.

Portions of this polymer are compounded with diisocyanate curing agents as shown in'tlie following table.

In each case, the polymer is milled to a smooth sheet ona rubber: mill, the: diisocyanate' having: one shielded' isocyanate group is milled in (except in control samplesA and: B in which? this compound. is. omitted:);. and then 1,BvbisK-B-isocyanatm4methylpheny13urea. isi milled in.

A portion is subjected to the 130 C. mill scorch-testL.

run on the compoundedstock. The resultsare shown.

below the compositions. The composition figuresdenote parts by weight.

Inspection..of;these datashows thatthe low readingds. roughly 101-12; points lower whenv the. 4.-methoxy. -m=.

The resultsvarej as follows; phenylene. dnsocyanate lS-xllSfld. and. thata. correspond-1 3 UnsymmetrlcaliDilsocyanate Parts of i Diisoey- Scorch No. anafioaryl v Time,- Remarks Parts/100 urea/100 Minutes. Type. parts parts- Elastorner- Elastomer 4 1 Fell 01f mnrm-z minutes. v -do 1.5 5-

2,4-tolylene diisoeyanate. 1. 5.. Band still smooth at 20 minutes. Mort;,butyl-m-pheuylene 1.6 1.5 Band still smooth diisoeyanate. and tacky: at1=25- minutesl E Phinethoxy-mmhenylene 1; 5'. Band still smooth diisocyanate at 30 minutes. F- i. 0 1.5 4.0 15 G- 10; c 0:5 320 12 It is apparent from these results that the" scorch resistanceis increased very substantially by the addition of the small amount of unsymmetrical diisocyanate.

Example 2.-

1300" parts of polytetram'ethyl'ene ether glycol having :an average molecular weight of 2420 and containing 0.02%, water and' 115 parts of 2,4-tolylene dii'socyanate are mixed in a Werner-Pfleiderer. mixer for 3.5 hours at 130 C; There are then added 22.4 parts of m-tolylene diamine and mixing is continued for an additional half hour. The mass is cooled and the elastomer removed from the mixer.

100. parts of. the polymer are milled to a smooth band on a rubber mill and 5 parts of 1,3'-bis(3-isocyanato-4- methylphenyDurea are milled in. This composition shows a 130 scorch time of '5 minutes.

Another 100 part portion of the polymer is milled to a smooth. band and 2 parts of 4-methoxy-m-phenylene diisocyanate are milled in. When this is thoroughly incorporated, 3 parts of 1,3-bis(3-isocyanato-4 methylphenyl)'urea are milled in. The 130 C. scorch time is longer than 15 minutes since when the test is discontinued at that time the band on the mill is still shiny and nervy and shows no indication of scorch.

Example 3 1350 parts of polytetramethylene ether glycol of molecular weight 2340and containing 0.28% water and.

211, parts of 2,4-tolylene diisocyanate are mixed in..a. Werner-Pfleiderer. mixer at 70 C. for 3. hours. There arethen added 53.1 partsof water ann1iXing is C011-,

tinued. for an additional 28 minutes duringwhichitime,

ingly longer timeof. millingds-permissible before the value reaches 50.

Example. 4

215 parts of polytetramethylene ether glycol of. aver? age molecular weight 970Iand' 26 parts of 2.,4-tolylene diisocyanate are mixed together in a. W'e'rner-Pfieid'erer.

mixer, at C. for 3'.hours. Thepolyurethanethus formed having terminal hydroxyl groups and a molecular, weight of32'60' is cooled at 70175' C. and013'6. part "of,

water, is mixed; in.. 291-6 parts, of 2,4Ft'olyl'ene1 dii'slocyanate are added" andmixing is continued for an additional Z'hours at: 70-75 C. There are then added 9.3.

parts of water and mixing is continued for 19 .miriutes. The temperature rises to 100 C. The rubbery mass is discharged. from the mixer and milled; on a rubbermill 1 with 1.85parts of piperidi'ne to form a stabilized poly: mer. The elastomer is then sheeted off the mill.

The polymer is compounded in three batches on a rubber mill as follows (parts being by weight);

v A j B A C Elast omer 100 100 100 ZA-Tolyl'ene' diisoeyanate t 1 4-Methoxy-m-phenylene diisocyanate L. 1,3bis(3-isooyanat0-4-methylpheny1)urea 4 4 4'.

In samples B and C, the first diisocyanates are thor:

oughly milled in before the urea is added; this requiring about 1015 minutes at a mill roll temperature of" scorchi'ness; The-observed readings are given in the;

table below.-

Elapsed Time, Minutes Inspection of the table shows the considerable improvement in scorch properties resulting from addition of the partially hindered diisocyanates.

Example (A) Preparation of polyurethane.950 parts of poly tetramethylene ether glycol of molecular weight 945 containing 0.02% water and 117.5 parts of 2,4-tolylene diisocyanate are stirred together for 3 hours at 100-105 C. The resulting polyurethane has hydroxyl end groups, a molecular weight of 3180, and no free NCO groups.

(B) Preparation 0 elasromer.2775 parts of polytetramethylene ether glycol of molecular Weight 925 and 351.5 parts of 2,4-tolylene diisocyanate are stirred together at. 100-105 C. for 3 hours. 200parts of the resulting viscous liquid are put in a Werner-Pfleiderer.

mixer with 0.36 part of water and mixed for 15 minutes while the temperature is adjusted to 70-75 C. Then 23.3 parts of 2,4-tolylene diisocyanate are added and mixing is continued for 2 hours at 70-75 C. 8.06 parts of Water are added and mixing is continued for 20 minutes while the temperature increases from 70 C. to 100 C. The rubbery mass is removed from the mixer promptly and milled on a rubber mill where 0.18 part of piperidine is added per 100 parts of polymer for the purpose of stabilization.

(C) Preparation andtesling of compounded stock.-- The following formulations are compounded on a rubber mill (parts being by weight):

The ingredients are added to the mill rolls in the order shown.

These two stocks are subjected to the extruder scorch test described above. Sample I extrudes significantly longer than sample 11. Sample II begins to show signs of scorch at 25-30 minutes, while sample I does not show signs of scorch until 4550 minutes. The temperature in these tests ranged from about 140 C. to 150 C.

The Mooney scorch figures at 100 C. on these two stocks are:

These tests also show the improvement in scorch prop erties caused by the preliminary addition of 4-methoxym-phenylene diisocyanate.

Example 6 2730 parts of polytetramethylene ether glycol of molecular weight 910 and 351.5 parts of 2,4-tolylene diisocyanate are stirred together for 3 hours at -105 C. to form a polyurethane having a calculated molecular weight of 3078. h

200 parts of the polyurethane are placed in a Werner- Pfleiderer mixer and mixed with 0.37 part of water for 15 minutes at 70 C. Then 26 parts of 2,4-tolylene diisocyanate are added and mixing at 70-75 C. is continued for 2 hours. 8.2 parts of water are added and mixing is continued for an additional 25 minutes while the temperature rises from 70 C. to 100 C. The rubbery mass is then removed from the mixer and sheeted out on a rubber mill while 0.66 part of piperidine per 100 parts of polymer is milled in to stabilize it.

The polymer is peptized to reduce its viscosity by blending in 0.25 part of N-methylethanolamine for each 100 parts of elastomer on the rubber mill and transferring to the Werner-Pfleiderer mixer Where it is mixed for 15 minutes, the temperature-rising from 100 C. to C. Cooling is necessary at the latter part of the mixing to keep the temperature at 135 C. The charge is removed from the mixer in the form of rubbery chunks which are sheeted ofi the rubber mill in a smooth sheet.

Portions of the elastomer are compounded by first milling the polymer at 100 C. on a rubber mill for 10 minutes, adding the 4-substituted m-phenylene diisocyanate as shown in the table and milling for 10 minutes at 100 C., and finally milling with 1,3-bis(3-isocyanato-4- inethylphenyD-urea for 10 minutes at 100 C. A Mooney scorch test is then run on the sample using the small rotor at 100 C. The compositions and results of the scorch test are shown in the table below (parts are by weight) It is apparent that the processing safety from the scorch standpoint is increased from 50 to about 200% by the use of the two different types of diisocyanates.

Although this invention is particularly useful andhas been illustrated with particular reference to elastomers formed from polyalkylene ether glycols, diisocyanates and chain extending agents, it has application generally to the curing of any elastomeric materials composed of polymeric chains containing reactive hydrogen atoms and which may be cured by cross-linking at the active hydrogen sites.

The process of this invention in which diisocyanates of different type are added in turn as curing agents unexpectedly permits longer milling of the polymer without scorching than is possible with either type of diisocyanate alone. Some uncured elastomers of the type here considered may be milled to a smooth band on a cold mill, i. e., one to which no heat is applied, although the actual temperature may build up to as high as 50 C. by friction. On the other hand, with some elastomers it is necessary to heat the mill to around 100 C. in order to obtain a smooth band. The tendency for scorching to take place is greater at the higher temperatures and under these conditions the use of the two-step process here described is of particular value.

. elastomers.

Thescuredielastomersprepared according to.-the. present process. (may the used; c for the. wsamempurposesaas other. From them may be prepared such articles,

as tires, inner tubes, belts, hose and tubes, wire and cable jackets, footwear, sponge,'coated fabric and various other molded orlfdippedzarticless. a

The, basic ,elastomeric properties of these products: may be varied; by; suitable q compounding The'1type-randi? amount oftthez-compounding agent to-be-11sed is dependent j upon the use for which the elastomer is intended Some) of the. m ore. important compounding; agents which are of value.-with.-thcse elastomers:arescarbonblaclc, clay silica talcezinc andtmagnesiumloxides, calcium and mag- I nesium titanium \dioxide and ;plasticizersi Inorganic: ands:

organic coloring-,-agents;-may .be-incorporated;to-give well,-

defined-colored'productsi, The natural colonof, the elastomenis a. pale yel-1ow or a .light'; amber.

The compounding agents may be mixed orincorporated with. the rproductsat athev-same time th'atlthe idiisocyanate 1. vulcanizing agents aresaaddede Conventional rubber processing machinery suchaas rubberpmills; and Werner? Pfleiderer or Banburymixersmay be used.- The; resulting compounded stocks maybe shaped or cured in con Alternatively-thew I stocks may-fibedissolvedor extended with V solvents for application to, surfaces-mpon -which, they may be cured;

ventional rubber industry; equipment;

after. evaporation of the solvent.-

What is claimed is:

l; The process of'curing a stable uncured polyurethane reactionproduct, which is-curable by heating-with; a

polyisocyanate and ,whichcontains substantially'no .free': isocyanate; groups, said polyurethane reaction; produota containing; a: plurality of; intralinear radicals oi thG 'fOIrmulazwhereinhtheflbivalent radical O,-G.--O- is obtained. by removing the terminal hydrogen atoms of a polymeric, glycol, said glycol having a molecular weight of at least 750 and being selected from the group consisting of polyalkylenecthert glycols, polyalkylene-aryleneether glycols, polyalkylene-cycloalkyleneether glycols, polyalkyleneether-polythioether glycols, poly-aliphatic hydrocarbon;

glycols and polyester glycols 1. of the formula or H C by weight of, an, arylene.v diisocyanate, of. theiofmula wherein-R i's-selected from the groupconsisting of lower alkyl, lower alkoxy arid'chlor-ine, and heating :the -mi-xture-to--a temperatureof from ab'out 90 to 150- C; until a cured elastomer-is fo'rmedi 2. The 'process' of clai'm -1 in=which-the diis'ocyanate having-only; one-'isocyanategroup ortho to a 'substituent' on the :aromatic ringis '2 ,4-tolylenedii'socyanate.=-

3; The process iof claim' l in whichthe diisocyanatehaving "only oneisocyanategroup- 'orthoto asubstituent on 'thearomatic ring is4-methoxy-m-phenylene diis"ocyanatez- 4'. In theprocess-of'curing a stable uncured polyurethane reaction product which-is curable byheat-ing with a polyisocyanate an d,wh i ch containssubstantially no free isocyanate groups, saidpolyurethane reaction product--- ontaini g atp u i y of nearz' dira smfifih mula,

wherein the bivalent radicalO?G O-fi'is.obtained-- by'removing the terminal hydrogen atoms of'a polymeric glycol, said": glycol. having -a molecular weight ofaLleast- 750 and being selected ifrom the group consisting of poly:

alkyleneether glycols, ,polyalkylene-aryleneether glycols, polyalkylene-cyclojalkyleneether glycolsand polyester glycols of the-formula- 0v 7 noiipo-o (Lo n-orrv wherein Rrand are. hyd.rocarl1onradicalsland.nuismmnv integer, the steps which'comprise thoroughlyblending' by milling with the said'reaction product from. 0;!jtq

2% by weight of an, arylene diisocyanate in which one only of the isocyanategroups is-ortho to a ,substituent J on the aromatic ring, said'substituent being selected'from the group consisting of lower-alkyl, lower alkoxy and phenoxy radicalsandhalogen atoms .andw thereaften in,

corporating: by milling from 1 to -20% byiweight'of; am-

arylenerdiisocyanateof the formula where-in' R- is-selected' from the groupeconsisting of l lower alkyl; lower-=alkoxy; and; chlorine and thereaften heating to a-ternperature of fromabout 90-to Guntil am elastomer is formed.

5; The process of-c1aim*4 in which the diisocyanate havingone only-of its isocyanate groupsorthotoasub stituent on-the aromatic ring has theformula I NCO in whichsR'is amember of the class consisting o f3-ldwer; alkyl, lower alkoxy and phenoxy radicals, and halogen atoms 6. The process ofclaim 5 in whichthe uncured poly urethane reaction product is formed-from the reaction of a polyalkylene ether glycol having a molecular weight of at least 750, a molar excess of an organic diisocyanate, and a chain: extending agent containing a plurality of active hydrogen atoms, no more than two atoms in the moleculei'having active hydrogen attached thereto,

72 Theiprocess of curing a stable uncured; reaction product, of a polytetramethylene; ether; glycol havinga, molecular weight of at least 750, a molarexcess of tolylene diisocyanate and .water, said reaction product containing substantially no free isocyanate groups; which comprises thoroughlyblending therewith by milling from 0.5,to,v 2% byvweightvof 2,4-tolylene diisocyanate, there:

after incorporating, vby milling from 1 to 20% of;"'1',3 bis(3-isocyanato-4 methylphenyl)urea and. heating thei mixture atat temperaturebetween, 90 and 150? 'C. toproduce, a vulqanized elastornen- 8. The process 'of curing a stable uncured reactiqng;

p oductob po yt ram hy ene e e ly l a g molecular weight of at least 750, a molar excess o f tolylenediisocyanate and water, said reaction product containing substantially no free isocyanate groups, which prises. thoroughly blendin therewith by g om 0.5. -to 2% by weight of 4-methoXy-m-phenylene cyanate-,'t-hereafter incorporatingby. milling-:fronnu; 20% of-- l,3-bis('3-isocyanato-4-methylene)urea and,

glycols, polyalkyleneetherpolythioet-her glycols, poly-aliphatic hydrocarbon sglycols, halogen-substituted poly-aliphatic hydrocarbon 13 heating the mixture at a temperature between 90 and 150 C. to produce a vulcanized elastomer.

9. The process of curing a stable uncured reaction product of a polytetramethylene ether glycol having a molecular weight of at least 750, a molar excess of tolylene diisocyanate and Water, said reaction product containing substantially no free isocyanate groups, which comprises thoroughly blending therewith by milling from 0.5 to 2% by Weight of 4-chloro-m-phenylene diisocyanate, thereafter incorporating by milling from 1 to 20% of 1,3-bis(3-isocyanat0-4-methylphenyl)urea and heating the mixture at a temperature between 90 and 150 C. to produce a vulcanized elastomer.

10. The process of curing a stable uncured reaction product of a polytetramethylene ether glycol having a molecular weight of at least 750, a molar excess of tolylene diisocyanate and water, said reaction product containing substantially no free isocyanate groups, which comprises thoroughly blending therewith by milling from 0.5 to 2% by Weight of 4-phenoXy-m-phenylene diisocyanate, thereafter incorporating by milling from 1 to 20% of 1,3-bis(3-isocyanato-4-methylphenyl)urea and heating the mixture at a'temperature between 90 and 150 C. to produce a vulcanized elastomer.

11. A cured elastomer obtained by the process of claim 1.

12. A process according to claim 1 in which the heating step is carried out in a mold under pressure to form a shaped, vulcanized elastomer.

13. A shaped, vulcanized elastomer obtained by the process of claim 12.

14. The process of claim 1 in which the bivalent radical OGO in the polyurethane reaction product is obtained by removing the terminal hydrogen atoms of a polyalkyleneether glycol.

15. The process of claim 14 wherein the polyalkyleneether glycol is a polytetramethyleneether glycol.

References Cited in the file of this patent UNITED STATES PATENTS 2,531,392 Breslow Nov. 28, 1950 2,625,531 Seeger Jan. 13, 1953 2,692,873 Langerak et al. Oct. 26, 1954 2,749,960 Schwartz June 12, 1956 2,777,831 Seeger et al. Jan. 15, 1957 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Noo 2,858,,296 October 28, 1958 Frederic Bo Stilmar It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 24, for "substitute" read substituents column 6, line "62, TQr D Ol V'F" read w D==l077= column 8, line 44, for "at" read to column ll, line 45, after "glycols", first occurrence, insert -=,halogen-substituted poly-aliphatic hydrocarbon glycols o Signed and sealed this 10th day of February 195% (SEAL) Attest:

KARL Ho AXLINE f ROBERT C. WATSON Attesting Oflicer Commissioner of Patents 

1. THE PROCESS OF CURING A STABLE UNCURED POLYURETHANE REACTION PRODUCT, WHICH IS CURABLE BY HEATING WITH A POLYISOCYANATE AND WHICH CONTAINS SUBSTANTIALLY NO FREE ISOCYANATE GROUP, SAID POLYURETHANE REACTION PRODUCT CONTAINING A PLURALITY OF INTRALINEAR RADICALS OF THE FORMULA 